Examination of one of MESSENGER's solar panels during testing activities

Two single-sided solar panels are the spacecraft’s main source of electric power. To run MESSENGER’s systems and charge its 23-ampere-hour nickel-hydrogen battery, the panels, each about 1.5 meters (5 feet) by 1.65 meters (5.5 feet), will support between 385 and 485 watts of spacecraft load power during the cruise phase and 640 watts during the orbit at Mercury. The panels could produce more than two kilowatts of power near Mercury, but to prevent stress on MESSENGER’s electronics, onboard power processors take in only what the spacecraft actually needs.

The custom-developed panels are two-thirds
mirrors (called optical solar reflectors) and one-third triple-junction solar cells, which convert 28 percent of the sunlight hitting them into electricity. Each panel has two rows of mirrors for every row of cells; the small mirrors reflect the Sun’s energy and keep the panel cooler. The panels also rotate, so MESSENGER’s flight computer will tilt the panels away from the Sun, positioning them to get the required power while maintaining a normal surface operating temperature of about 150°C, or about 300°F.